Miniaturization and portability for electronic products including home appliances in recent is quickly going on. In addition, the transmission for all information and signals is wirelessly processed and the lines to be connected to equipments disappear. The trial for wirelessly transmitting the power is performed in case of home appliances. In more detail, the wireless power transmitting using electromagnetic induction is used in an electric toothbrush, etc., but there are problems in that the transmitting efficiency is too lowered, even when the distance is slightly increased, and unnecessary and dangerous heat generation are caused.
On the other hand, a recent studying non-radiative energy transmitting technology, that is, an electromagnetic resonant wireless power transmitting scheme may acquire high transmitting efficiency even at the distance of many meters as compared with the existing electromagnetic induction scheme. This technology is based on attenuation waves coupling for moving electromagnetic waves from one medium to another medium through local area electromagnetic fields on resonating two media as the same frequencies from each other, and therefore the energy is transferred only when the resonant frequencies between two media are the same, and the unused energy is reabsorbed into electromagnetic fields. Therefore, the electromagnetic waves are harmless to peripheral machines or humans differently with different electromagnetic waves.
FIG. 1 schematically shows a wireless power transmitting system according to a prior art. As shown FIG. 1, a electromagnetic resonant wireless power transmitting scheme according to a prior art includes a power supply section A, a transmitting resonant coil S for receiving the power by inductive coupling with the power supply section A, a receiving resonant coil D for receiving the power by magnetic resonance with the transmitting resonant coil S, and a load end B for finally receiving the power by inductive coupling with the receiving resonant coil D.
The transmission having high efficiency is possible in the electromagnetic resonant wireless power transmitting system according to the prior art when the resonance frequencies between the transmitting resonant coil and receiving resonant coil should be correctly coincided from each other. In addition, the impedance matching between the transmitting coil and receiving coil is necessary at the transmitting frequencies, and therefore the distances between the transmitting coil and power supply and the receiving coil and load end should be suitably controlled according to the transmitting distance.
In order to solve those problems, Korean Unexamined Patent Application Publication No. 2011-0062841 has proposed a wireless power transmitting apparatus including at least one power relay coil to wirelessly transmit the power to a plurality of electronic equipments positioned at a long distance.
However, the wireless power transmitting scheme using a prior magnetic resonance has a limiting item in that the power supply section and the transmitting resonance coil must transfer the power in an inductive coupling type.
The wireless power transmitting scheme using the magnetic resonance according to the prior art has problems in that the resonant frequencies may be affected by an antenna of the power supply section and mutual inductance of the transmitting coil.
Further, there is a limit for a long distance transmitting, a variable RF impedance matching circuit separately needs according to the distance from the load impedance, and there is a difficulty for implementing the transmitting section with multi-channel. The wireless power transmitting scheme using the magnetic resonance according to the prior art has to include the power supply section for each transmitting section so as to implement the transmitting section with multi-channel, thereby to increase the manufacturing cost of the system.